Back pad structure



Jan. 27, 1970 J. H. M 'KAY, JR

-BACK PAD STRUCTURE Filed May 6, 1966 United States Patent 3,491,494 BACK PAD STRUCTURE Joseph H. MacKay, Jr., Woodland Hills, Calif., assignor to Standard Abrasives, Inc., a corporation of California Filed May 6, 1966, Ser. No. 548,186 Int. Cl. B2441 17/00 Us Cl. 51--358 8 Claims ABSTRACT OF THE DISCLOSURE A pad for supporting a rotary finishing article. The pad has a surface adapted to slidingly engage the finishing article and said surface has a low coefiicient of friction. The pad also includes means for attachment to a rotary drive means.

The present invention relates to an improved back pad structure, as for supporting abrasive discs and other finishing articles, during rotary motion for grinding, sanding, abrading and like operations with power equipment.

A wide variety of structures for supporting and backing abrasive discs and other finishing articles when used on a power apparatus have been proposed in the past. Traditionally in the most common forms of such apparatus the finishing article, e.g. an abrasive disc, or the like, has been supported by a rubber-back pad in order to provide the desired degree of flexibility during operation. At usual operating speeds of typical abrasive products these rubber back pads have a tendency to diametrically grow. This diametrical growth to the back pad is undesirable and it has been traditional in the prior art to reinforce the rubber with fabric to overcome this problem. A typical manner in which the fabric has been inserted into the rubber is to directly mold the same into the pad at the time of its formation. In those instances wherein the fabric is positioned directly into the pad, formidable problems are presented in attempting to maintain the fabric at the desired spot. In most instances the fabric has a tendency to move upon the application of heat and pressure during the molding process. A movement of the fabric causes the rubber back pad to become dynamically unbalanced. Such unbalancing adds undesirable stresses to the power machinery during the rotation of the pad particularly at high speeds.

Furthermore in utilizing the rubber back pad of the prior art particularly in those areas wherein a finishing article is applied to the pad by a twisting or sliding -mo- I tion, it becomes extremely difficult to effect the sliding movement between the abrasive finishing article and the back pad due to the large frictional component therebetween caused by the face of the rubber.

As will be recognized by those skilled in the art the rubber back pad used in the past has been relatively fragile, that is subject to being scarred or damaged during use. Although such is not desirable it has been accepted as being somewhat necessary in order to accomplish the desired objects.

Accordingly, it is an object of the present invention to provide a finishing article holder incorporating a back pad, which is rugged, economical to manufacture, aflfords good balance characteristics, and which permits replacing the finishing article with relatively little effort.

It is another object of the present invention to provide a back pad and related structure for holding a finishing article, which avoids gripping relationship between the back pad and the finishing article, whereby to facilitate changing the finishing article, and providing a durable back pad of good capability for feathering operations.

It is another object of the present invention to provide an improved finishing-article back pad which may be used for extended periods without heat damage, and

which avoids gripping relationship between the finishing article and the back pad, for better operation characteristics as well as ease of changing a finishing article otherwise affixed to a rotary drive member.

As a further object of the present invention to provide a back pad which is extremely simple to mold, which is dimensionally stable and which is perfectly balanced at all times irrespective of the speed of rotation thereof.

It is still a further object of the present invention to provide a back pad for supporting abrasive finishing articles in which the reinforcing fabric is stabilized and in which the reinforcing fabric is in itself reinforced,

One other object of the present invention is to provide a finishing-article holder including a rotary drive means which positively engages the finishing article, the back up support for the finishing article being provided by a back pad including a central attachment structure for positive coupling to the drive means, an imperforate resilient layer, having a flat, hard, smooth (having a low coeflicient of friction) surface extending outward from the central attachment structure, for receivably engaging the finishing article; and a resiliently-deformable body backing the layer and furthermore afiixing the layer to the central attachment means.

It is still another object of the present invention to provide an improved back pad for supporting a finishing article in which the flexibility thereof can at the time of manufacture be controlled by varying the compound of the rubber used therein or by varying the thickness of the resilient layer bonded to the rubber.

Other objects and advantages of the present invention will become apparent from a consideration of the follow ing description taken in conjunction with the accompanying drawings which are provided by way of example only and are not intended as a limitation upon the scope of the present invention as defined in the appended claims, and in which:

FIGURE 1 is a perspective view of a rotary finishing apparatus having an abrasive finishing article attached thereto and incorporating the present invention;

FIGURE 2 is a partially exploded perspective view of the structure of FIGURE 1;

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2.

Referring now to the drawings, and more particularly to FIGURE 1 thereof, there is shown a finishing apparatus 10 including a circular abrasive finishing article 11 attached to a mating support and drive structure. A drive shaft 14 extends axially from the structure 12 and may be variously affixed to a rotary power tool (not shown) for revolving the finishing article 11. The shaft 14 may be revolved at relatively high speeds to drive the finishing article 11 and thereby accomplish various grinding, sanding or abrading operations, during the course of which the finishing article 11 is supported by a back pad 16 as more specifically described in detail below.

The finishing apparatus 10 employs a finishing article 11, which carries effective abrasive over one entire surface thereof. That is, the finishing article 11 does not define a central aperture through which it is clamped to the back pad 16. Rather, the finishing article 11 is aflixed to the back pad 16 by engagement with fingers or tabs 18 (FIGURE 2) extending from the rotary drive structure 20. Specifically, the tabs 18 are matingly received in arcuate openings 22 defined in a raised coupling 24 which is bonded to the rear or internal surface 25 of the finishing article 11. Thus, the extending tabs 18 mate within the openings 22 then relative rotation couples the finishing article 11 to the driving structure 20 by hooking the tabs 18 into the coupling 24. This positive locking arrangement accomplishes firm coupling between the elements and one form thereof is fully explained and Patented Jan. 27, 1970 3 shown in, detail in US. Patent 3,158,972 issued Dec 1, 1964 to Joseph A. MacKay, Jr. and Melvin'l McKellar. Considering the detailed structure of an illustrative back pad which functions in cooperation with the elements considered above or equivaients thereto in accordance with the present invention, reference will now be made to FIGURE 3. The rotary drive structure includes the shaft 14 having a threaded section 26, and an integral enlarged cylinder 28, from which the tabs 18 extend. An annular rim'30 is formed at the lower end of the cylinder 28 defining an upward facing annular shoulder 32 about the cylinder 28. The cylinder 28 is then telescopically received in a cylindrical ring 34 having an internal shoulder 36 which matingly abuts the shoulder 32, of the cylinder 28.

The upper end 38 of the ring 34 engages a coil spring 40 which is confined between the ends 38 and the upper end closure 39 of the cylinder 42, having an open lower end and telescopically receiving the cylinder 28 with the threaded section 26 of the shaft 14 threadably engaged with a bore 44 of the closed end 39. The exterior of the cylinder 42 carries a threaded section 48 upon which the back pad 16 is received.

Considering the back pad 16 in detail, an internai or central ring 50 is internally threaded to receivably engage the threaded section 48 of the cylinder 42. The ring 50 includes" an annular flange 52 which mates with an externally tapered circular body 54 of rubber-like material, the lower surface of which is bonded to a hard-surfaced substantially uniform layer 56.'The layer 56 may be formed for example of phenolic mate-rial, e.g, reinforced theremo-setting' phenolic laminate. In such instance, the layer 56 may include fiber glassjfabric or other material which is impregnated with phenolic resin and then cured, for reinforcement. In .such manner the reinforcing material is reinforced by the resin. The layer 56 is bonded to the body 54 which is in turn bonded to the contained ring 52. In this regard, it is to be noted that the rigid ring 52, normally formed of metal, is not directly corrnected to, or contacted by the layer 56. As a result, the body 54 of resiliently-deformable material affords some flexibility in coupling between the more rigid elements. It is also to be noted that the ring 50 is substantially completely embedded in the body 54 with the result that'an external shoulder 60 in the body 54 is provided exterior of the ring 50. The reduced thickness section 62 ofthe body 54 then extends coextensive with the layer 56 and is thicker than the layer 56 In manufacturing the back pad 16 as shown in FIG- URE 3, a heat and pressure mold may be employed which defines a cavity substantially coinciding to the shape of the composite .back pad. Initially, the layer 56, formed in a separate rnold as by heat and pressure is laid into the rfiold under consideration, sthen the ingredient of the body 54, neoprene rubber for example, is placed in the mold along with the ring 50 which forms the central attachment means. Thereafter the mold under consideration is closed and heat and pressure are applied to the contents to cure the body 54, bonding it to the layer 56 and the central ring 50. The body 54 is thus faced by the imperforate somewhat-resilient layer 56 which provides a hard tough surface 65, having little or no tendency to grip or grab the attached finishing article that is, a surface with a low coefficient of friction.

It is to be noted, that although various dimensions are feasible and have been successfully used, it has generally been found desirable to provide the body 54 at least as thick as the layer 56. Such dimensions afford effective operation in cooperation with the flexure provided by the structural arrangement wherein the ring 50 is axially displaced within the body 54 from the layer 56.

If it becomes desirable to provide more flexibility for the pad, such can be accomplished by making the layer 56 thinner. Alternatively such can be accomplished by using a softer rubber in the body 54. Of course it will be recognized that by either selecting a harder rubber for the body 54 or a thieker layer 56 the pad can be made stiffer if such is desired. e

In using the illustrative structure hereof, a finishing article 11 (FIGURE 2) of circular form and comprising abrasive paper for example, is placed on the circular back pad 16 by engaging the tabs 18- within the openings 2 2 and revolving the article 11 relative to the back pad 16, to hook the tabs into the coupliiig 24.

In this regard, the spring 4?) (FIGURE 3) exerts a downward force on the ring 34" which further locks the finishing article 12 to the drive structure. The manual placement of the finishing article in engaging relationship involves pressing the finishing article 11 so that the coupling 24 (FIGURE 2) receives the tabs 18 through the openings 22 then manually revolving the finishing article to mate the tabs 18 into the openings 22. This revolving operation may be easily performed in view of the fact that the hard surface of the layer 56 does not grip or hold the back of the finishing article 11.

The composite finishing apparatus may now be effectively used and in view of the hard mating surface 65 of the layer 56, the finishing article 11 is afforded good support yet permitted'freedom to moveiinto various conforming relationships; This consideration is particularly important with respect to some operations. Good balance characteristics, as well as durability are also provided.

At the conclusion of a period of using a finishingarticle 11, it may be simply and easily removed by counter-revolving it to disengage the tabs 18 (FIGURE 3). Again, the hard non-gripping surface 65 of the layer 56 permits this operation to be accomplished manually with ease and simplicity.

Thus, the back pad structure as provided herein is economical to manufacture, durable and rugged, and furthermore provides improved characteristics backing a finishing article. Although a specific embodiment of the structure for finishing has been described and illustrated above, it is expressly emphasized that various changes may be made in a structure hereof without departing from the scope or spirit of the present invention as defined in the appended claims. I

i What is claimed is:

1. A back pad structure for use with a finishing article which rotates with respect to the back pad structure when being attached thereto, for use with a rotary drive means, comprising: i

attachment means centrally disposed in said back pad and including coupling means for cooperatively engaging a drive member aflixed to said finishing article by relative rotation between said finishing article and said coupling means;

a resilient layer having at least one smooth surface having a low coefficient of friction and adapted to slidingly receive a finishing article to be attached to said back pad structure for receivably engaging said finishing article and facilitating rotation thereof during attachment thereto, said layer defining a central aperture therein; and

a resilientiy deformable body backing said layer on the side opposite said smooth surface and being bonded permanently thereto, said body being permanently afiixed to said attachment means.

2. A back pad structure according to claim 1 wherein said resilient layer comprises a hard surface phenolic material, the surface opposed to that for engaging said finishing article being surface bonded to said resiliently deformable body.

3. A back pad according to claim 1 wherein said body comprises a rubber-like material having a minimum thickness of at least the thickness of said resilient layer.

4. A back pad according to claim 3 wherein said central attachment means, said resilient layer and said body are generally circular and held concentric by bonds of said rubber-like material.

5. A back pad according to claim 4 wherein said imperforate resilient layer comprises reinforced thermosetting phenolic laminate.

6. A back pad according to claim 1 wherein said central attachment means, said resilient layer and said body are generally circular and held concentric with said central attachment axially displaced from said resilient layer by said body.

7. A back pad according to claim 6 wherein said rubber-like body is co-extensive with said layer.

8. A back pad structure according to claim 7 wherein said layer comprises a hard-surface phenolic material.

. References Cited UNITED STATES PATENTS Wiley 51-358 Welch 51-37-8 Reames 51378 Sopcak 51-378 X Block 51-358 Purcell 51-376 10 ROBERT c. RIORDON, Primary Examiner DONALD G. KELLY, Assistant Examiner 

